1. Field of the Invention
The present invention relates to a sheet discharge device having a plurality of levels of sheet discharge trays, that is, a multi-tray device, and an image forming apparatus in which this sheet discharge device is applied.
2. Description of the Related Art
An image forming apparatus performs a predetermined image formation processing based on image information acquired by reading an original image or one transferred from the outside, and then performs print processing on paper (sheet) according to this image information. Paper on which print processing is performed is immediately discharged, or is discharged after post-processing, such as punching processing and stapling processing.
Some image forming apparatus have a multi-tray device, in which a plurality of paper discharge trays are installed in vertical parallel positions as paper discharge destinations. In an image forming apparatus having a multi-tray device, discharge paper conveying paths are provided along the edge of each paper discharge tray in the vertical direction.
Japanese Patent Application Laid-Open No. H4-308865, for example, discloses a multi-tray device in which switching guides (distribution guides) for switching the paper conveying destination between the paper discharge path and the paper discharge tray, and solenoid devices for changing the orientation of each switching guide, are disposed on the paper discharge path at a position facing each paper discharge tray. In such a multi-tray device, however, the solenoid device must be installed for each of the plurality of paper discharge trays, which increases the number of components and therefore increases component cost.
To solve this problem, Japanese Patent Application Laid-Open No. 2002-137866 discloses a multi-tray apparatus in which a gate is disposed in each paper discharge path, without disposing the respective switching guide and solenoid device in the plurality of paper discharge trays. This gate is rotatably supported with the rotation support point formed on a wall surface on one side of the paper discharge path, and the top edge thereof contacts the wall surface on the other side of the paper discharge path by the biasing force of the biasing means. When paper ascends the paper discharge path, the paper moves while opening a gate by the ascending operation, and when paper descends, the paper is always received by a gate and discharged to a paper discharge tray corresponding to this gate. In this device, a paper discharge tray at the paper discharge destination is selected in advance, and immediately after the rear end of paper passes through the gate corresponding to the selected paper discharge tray, this paper is conveyed in reverse. Thereby the paper is discharged and guided to the gate, and discharged to the target paper discharge tray.
However, in the case of a multi-tray device that requires the reverse conveying of paper, paper is unnecessarily conveyed in the forward direction until the rear end of the paper passes through the gate for the selected paper discharge tray, and then is reversed and discharged to the paper discharge tray. As a consequence, it takes an unnecessary amount of time to discharge the paper, for the amount of extra forward conveying and reverse conveying, and paper discharge efficiency is not good.